Concrete for a 32×40 slab
15.8 cubic yards (783 × 80 lb bags)
for a 32×40 ft slab 4 inches thick: 426.7 cu ft. Bag counts include 10% extra; at 6 inches you need 23.7 yards.
A 32×40 foot slab covers 1280 square feet. At the standard 4 inch thickness for a patio, walkway or shed floor, that is 426.7 cubic feet of concrete, or 15.8 cubic yards. At this size ready-mix is cheaper and far less work than bags: about 17.5 yards, roughly $2,888 before delivery fees, against $5,090 for 783 bags of 80 lb mix.
Concrete for a 32×40 slab by thickness
| Thickness | Cubic yards | Cubic feet | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|---|
| 3 in | 11.85 | 320 | 587 | 783 | 1174 |
| 4 in | 15.8 | 426.7 | 783 | 1043 | 1565 |
| 5 in | 19.75 | 533.3 | 978 | 1304 | 1956 |
| 6 in | 23.7 | 640 | 1174 | 1565 | 2347 |
| 8 in | 31.6 | 853.3 | 1565 | 2086 | 3129 |
Bag counts include 10% extra for spillage and uneven ground. Cubic yards and cubic feet are the exact volume.
How it’s worked out
- Convert the thickness to feet: 4 in ÷ 12 = 0.333 ft.
- Multiply length × width × thickness: 40 × 32 × 0.333 = 426.67 cu ft.
- Divide by 27 for cubic yards: 426.67 ÷ 27 = 15.802 cu yd.
- Add 10% and divide by the bag yield: 469.33 ÷ 0.6 = 783 bags of 80 lb mix (rounded up).
Under the slab, plan on 4 inches of compacted gravel: about 15.8 cubic yards. For driveways and anything that carries a vehicle, go to 5 or 6 inches and add rebar or wire mesh.
Change the numbers
Other slab sizes
- 30×40 slab
- 32×36 slab
- 28×40 slab
- 36×40 slab
- 26×40 slab
- 32×32 slab
- 25×40 slab
- 24×40 slab
- 30×32 slab
- 32×50 slab
- 40×40 slab
- 28×32 slab
Questions
- How many bags of concrete do I need for a 32×40 slab?
- At 4 inches thick, a 32×40 slab takes 783 bags of 80 lb concrete mix, 1043 bags of 60 lb mix or 1565 bags of 40 lb mix, including 10% extra.
- How many yards of concrete for a 32×40 slab?
- 15.8 cubic yards at 4 inches thick, 19.75 at 5 inches and 23.7 at 6 inches, before adding extra for waste.
- How much does a 32×40 concrete slab cost?
- The concrete alone for a 4 inch 32×40 slab costs about $5,090 in 783 bags of 80 lb mix (at about $7 a bag) or about $2,888 for 17.5 yards of ready-mix (at about $165 a yard, before delivery fees). Professionally poured slabs usually run $6 to $12 per square foot, about $7,680 to $15,360 for 1280 sq ft.
- How much does a 32×40 slab weigh?
- About 30.9 tons at 4 inches thick (concrete weighs about 145 lb per cubic foot).